1. Field of the Invention
The present invention relates to a light patterning device and method of using same.
2. Related Art
A patterning device is used to pattern incoming light. A static patterning device can include reticles or masks. A dynamic patterning device can include an array of individually controllable elements that generate a pattern through receipt of analog or digital signals. Example environments for use of the patterning device can be, but are not limited to, a lithographic apparatus, a projector, a projection display apparatus, or the like.
When imaging with micromirror arrays as the object, the phase of the light reflected by each mirror is critical. For example, when a flat tilting mirror is untilted (e.g., resting) light at the image plane and/or collected at projection optics is considered to have on average zero phase, i.e., has positive amplitude. During tilting of the mirror, there is an tilt angle at which no light on average is directed toward the image plane and/or is collected at projection optics, so the average amplitude of the light at the image plane goes to zero. Then, as the mirror continues to tilt, out of phase light reaches the image plane and/or is collected at projection optics, which is considered to be negative amplitude light. In conventional arrays of individually controllable elements having tilting mirrors, a maximum amount of negative light reaching the image plane is much smaller (e.g., of lower intensity or amplitude) than a maximum amount of positive light reaching the image plane.
When imaging with tilting mirrors, there can be a telecentricity error. Telecentricity can occur during patterning on an object as a pattern goes into and out of focus, and causes an image being formed to move/shift.
Currently, arrays of individually controllable elements can include various types of mirrors. Mirror types include, but are not limited to, flat tilting mirrors, single phase-step tilting mirrors, piston mirrors, or hybrid mirrors combining tilt and piston actions. However, because of intensity modulation constraints (e.g., unequal maximum amplitude of positive and negative light) these arrays cannot effectively emulate phase shifting masks and/or are inefficient when correcting telecentric errors. Individually, piston mirrors have a pure phase modulation effect, but amplitude modulation can also be obtained by combining piston mirrors into superpixels. A superpixel is formed when groups of pixels (e.g., 2×2, 4×4, or 8×8, etc) are combined to create one large pixel. This superpixel can collect increased amounts of light. This increases sensitivity (e.g., speed), but can sacrifice resolution. These superpixels can then behave as graytone pixels with the capability of achieving an intensity modulation anywhere between 100% positive phase intensity and −100% negative phase intensity. There are, however, as discussed above, limitations in replicating the effect of assist features smaller than the superpixel.
Another alternative, also discussed above, is a single phase-step tilting mirror (λ/4 height step and phase step of λ/2, where λ is an imaging wavelength), for example, by Micronic Laser Systems of Sweden. This mirror can achieve an intensity modulation anywhere between +50% and −50%. When at rest, no light enters a pupil of a projection system because, due to the step, half the light has a zero degree phase and the other half of the light has a 180 degree phase. As the mirror is tilted, light is captured or collected by the projection system, where a direction of tilt determines whether positive or negative light is captured or collected. Because of the symmetry of the single step mirror, equal amounts of positive and negative light can be captured or collected by the projection system. However, to correct for telecentric errors, the one step mirror requires alternating the position of the step (right or left), which is discussed below. This results in the dependence of the tilt angle sign on the position of the edge. This means that in order to achieve a given graytone with a particular mirror, the sign of the tilt angle needed requires knowledge of where the step is located, which creates an additional strain on the data path. In addition, mirror curling at the edges is likely to be exacerbated on a thinner side of the mirror and result in “tilt errors.”
Therefore, what is needed is an array of individually controllable elements, where each individually controllable element when used in the array has better positive and negative intensity characteristics and/or allows for effective and efficient telecentric error correction.